The present invention relates to a method for testing and filling semiconductor based liquid crystal displays, also known as liquid crystal micro displays (xe2x80x9clcmdsxe2x80x9d).
Lcmds are small liquid crystal displays that usually have a display area less than 1 square cm and a thickness of about 1 mm. They are primarily used as view finders in devices such as cameras but are also used as part of a larger display component wherein the image from the lcmd is projected or magnified. Each lcmd typically comprises hundreds of thousands of pixels but some can contain over a million.
Lcmd manufacturing is typically performed in a clean room environment wherein steps are taken to remove dust and other contaminating agents from the surrounding atmosphere. The degree to which a manufacturing environment is kept clean depends on factors such as the size and density of the integrated circuits contained in the lcmds, the desired quality of the lcmds, and the costs associated with maintaining different levels of cleanliness. Statistical models may be used to conduct a cost-benefit analysis for determining an ideal level of cleanliness for manufacturing lcmds of a certain type, size, and quality.
With reference to FIGS. 1 and 2 (prior art), each batch of lcmds is typically made from two substrates. Usually, one substrate is a semiconductor layer, such as a silicon wafer 9, containing many integrated circuits (xe2x80x9cICsxe2x80x9d) 12. Although, for illustration purposes, FIG. 1 shows that the silicon wafer 9 contains only nine ICs 12, each silicon wafer 9 typically contains hundreds of ICs 12 arranged in rows and columns. Each IC 12 includes an array of pixels comprising IC electrodes 16 driven via corresponding switching elements 17. The other substrate is typically a glass wafer 10 that has thereon one transparent electrode 15 per corresponding IC 12. Each substrate is typically, but not necessarily, less than 1 mm thick; the thickness of each substrate may vary according to the manner in which the lcmds are to be used.
A sealant that forms lcmd wall 11 is applied to one of the substrates. Traditionally, the wall 11 does not completely surround each IC 12xe2x80x94a small gap 13 remains through which the liquid crystal material flows to fill the lcmds. The silicon wafer 9 is then aligned and joined with the glass wafer 10 such that the transparent electrodes 15 are aligned with the corresponding ICs 12. Spacers (not shown) are used to keep the substrates separated by a small distance which is typically on the order of a few micrometers. The spacers may, for example, be etched onto the silicon wafer. After the substrates are joined, lcmds 8 are formed, each containing an IC 12.
Since the distance between the silicon wafer 9 and the glass wafer 10 is on the order of microns, viscosity limitations may make it impossible for liquid crystal material to reach many, if not most, of the inner lcmds 8 prior to their separation. Therefore, the lcmds 8 are filled with liquid crystal material via openings 13 after they are separated.
The lcmds 8 may be separated from each other by using, for example, a scribe and break process. In a scribe and break process, the semiconductor wafer 9 is scribed (typically with a specialized saw or laser) along scribe lines 14, in order to weaken the locations where the separation is to take place. In addition, the glass wafer 10 is scribed using a cutting tool such as a laser or a specially designed saw. The wafers 9 and 10 are typically then temporarily glued onto a flexible material that is then flexed in order to break up the wafers and separate the lcmds. The scribe and break process results in small debris of semiconductor and glass material that accumulate around lcmd openings 13.
After the lcmds are separated, they are filled with liquid crystal material. The filling is preferably achieved in a vacuum unit in which the lcmds are immersed in liquid crystal material. After an lcmd 8 is filled, the hole 13 through which it is filled is then sealed with a glue or epoxy material.
The traditional filling process described above often results in a large number of defective lcmds because debris from the scribe and break process are frequently pulled into many of the lcmds 8 by the in-flowing liquid crystal material. The debris may cause an electronic malfunction or may distort an image by blocking or altering the path of the electromagnetic radiation controlled by the lcmd. The defects caused by the debris are not discovered until after the lcmds are packaged since the packaging provides the wiring through which the lcmd receives imaging and testing signals.
Packaging an lcmd involves mounting and wiring. The lcmd is mounted into/onto a packaging unit at a predetermined angle and location so that the image produced is properly focused and aligned. The lcmd is also wired to terminals on the packaging unit. These terminals will eventually be connected to and will receive imaging and other signals from a host device, such as, for example, a camera. The area surrounding the wiring connections is typically filled with a glue or epoxy material that stabilizes the connections and prevents the wires from touching each other.
After the lcmds are packaged, they are tested so that defective units may be detected and eliminated. The testing can be difficult and costly since each individual lcmd must be tested separately. The reason that the lcmds cannot be tested while they are still part of a substrate assembly is because the testing must take place after the liquid crystal filling process (which has traditionally needed to be performed after the separation of the lcmds 8 due to viscosity limitations). The packaging process is relatively expensive and may account for most of the cost of a finished lcmd. Packaging the lcmds prior to testing significantly increases the cost associated with defective units since such cost would also include the cost of packaging.
Based on the foregoing, there exists a need for a system and method of manufacturing and testing lcmds that result in a higher yield and lower costs.
A liquid crystal micro display (lcmd) is manufactured by creating a hole in an lcmd surface, filling the lcmd with liquid crystal material through the hole, and then sealing the hole. The invention allows an lcmd to be tested before it is separated from other lcmds and packaged. As a result, the invention increases the yield and reduces the cost associated with lcmd manufacturing.